Debian

Debian is a widespread Linux release, that's used mainly on desktop machines, still many people have started using it lately as a web server Operating System as well, because of the stability and protection it offers. The latter is a direct result the fact that Debian is developed and supported by thousands of qualified volunteers around the globe, therefore any patch which is needed to fix a particular issue is released in a couple of days. The very same community will also help with any question or issue which a user may ever encounter, since they can be contacted via e-mail using mailing lists and a competent response will be sent in no more than 15-20 min. The advantage here is that your queries will be responded to by the same people who have designed the Operating System itself and they have a detailed knowledge of how it functions. As Debian is provided for free, you will not need to pay any kind of license fees to use it and you will be able to customize it as much as you want or need. This is valid for both the Operating System as well as the 30.000+ software packages which are readily available for it.